Abstract: :
Purpose: Evaluate the effect of light intensity in the workingenvironment on the retinal function, as measured with the electroretinogram(ERG). Methods: The retinal function of 9 outdoor workers (5W:4M; aged 23-40) was compared to that of 9 subjects working indoorsin an environment without windows (3W: 6M; aged 21-43). Eachparticipant had been working full-time (minimum 32hrs/week)in the same environment for at least 6 weeks (mean: 3.7 months).Light exposure was recorded 24hrs/day for a period of two weekswith an ambulatory monitor (Actiwatch®). ERG testings were conductedwith a LKC UTAS-E-3000 system which included a Ganzfeld of 30cm in diameter. The rate of dark adaptation was measured withflashes (average of 5) of -3.8 log cd.m-2.sec delivered every3 minutes for a period of 30 minutes. The time required to obtainthe maximal b-wave amplitude was considered as a measure ofthe rate of dark adaptation. After this 30-minute period ofdark adaptation, scotopic ERGs were recorded using 11 intensitiesof blue light (-5.01 to -0.96 log cd.m-2.sec). This was followedby the photopic ERGs recorded against a white background of30 cd.m-2 with the use of 15 intensities of white light (-0.80to 2.84 log cd.m-2.sec). Results: Indoor workers required lesstime for dark adaptation than outdoor workers (p=.07). Indoorworkers were also more sensitive in scotopic conditions (p<.005)but less sensitive in photopic conditions (p<.05) than outdoorworkers as revealed with the intensity needed to obtain therod and the cone b-wave Vmax. Furthermore, the entire photopicintensity-response function (photopic hill) was shifted towardsthe brighter flashes in the indoor group compared to the outdoorgroup, again showing a reduced sensitivity in the former group.Conclusion: The above results suggest that the light historyof our subjects influenced their retinal sensitivity to light.It would appear that a prolonged exposure to a low light levelincreased the sensitivity of the rods but decreased that ofthe cones. We might be looking here at the manifestation ofa photostasis process in humans. Animal studies on the photostasisphenomenon showed that the amount of photopigment adjusts inresponse to changes in the lighting environment in order toabsorb a constant amount of photons per day. Funded by CIHR,FRSQ, GRENE, NSERC and Réseau-Vision.